• ### Is time traveling possible you think?

191 answers · 1 week ago
• ### If an object moves 40 m north, 40 m west, 40 m south, and 40 m east, what's the total displacement? A. 80 m B. 0 m C. 160 m D. 40 m?

10 answers · 15 hours ago
• ### What if gravity on earth immediately turned to 200 times greater? Would we survive?

29 answers · 4 days ago
• ### Could the big bang have been the collision of two branes?

Best answer: That is a possibility that comes out of M-theory. Two 3-branes (3-dimensional structures that are the 3-d analogs to 1-d strings) separated by an extra dimension, collide with the resultant energy of the collision populating the 3-branes with energy. Of course, there is no evidence that m-theory is correct and... show more
Best answer: That is a possibility that comes out of M-theory. Two 3-branes (3-dimensional structures that are the 3-d analogs to 1-d strings) separated by an extra dimension, collide with the resultant energy of the collision populating the 3-branes with energy.

Of course, there is no evidence that m-theory is correct and obviously no evidence that 3-branes collided. It also doesn’t result the conceptual problems of why 3-branes existed prior to the collision..
8 answers · 21 hours ago
• ### Why hasn't a shrink ray been invented?

If all of our atoms were somehow reduced in size by the exact same ratio (that's the tricky part) we would survive it with no problems. We might even feel like the same weight. We'd just have to readjust to our "heavier" environment- and a lot less food- a crumb would feel very filling. Note that... show more
If all of our atoms were somehow reduced in size by the exact same ratio (that's the tricky part) we would survive it with no problems. We might even feel like the same weight. We'd just have to readjust to our "heavier" environment- and a lot less food- a crumb would feel very filling. Note that I didn't ask why an enlarging ray hasn't been invented. I would think that would be a whole lot harder to add mass than to remove it. Correct me if I'm wrong here.
10 answers · 2 days ago
• ### Tension In Elevator?

a = acceleration
T = tension
g = gravitational acceleration

@ rest or at constant speed
T = m*g

While acceleratin up or braking down
T' = m(g+a)

While acceleratin down or braking up
T'' = m(g-a)
a = acceleration
T = tension
g = gravitational acceleration

@ rest or at constant speed
T = m*g

While acceleratin up or braking down
T' = m(g+a)

While acceleratin down or braking up
T'' = m(g-a)
9 answers · 2 days ago
• ### What happens in the two-slit experiment if you use a detector that doesn't alter the experiment?

At first I was amazed by the mysterious way wave functions collapse by our mere knowledge of which slit they went through. Then I learned that essentially it's due to the measurement device firing photons on the electron, which is kinda lame because of course it isn't really the same experiment. Can we... show more
At first I was amazed by the mysterious way wave functions collapse by our mere knowledge of which slit they went through. Then I learned that essentially it's due to the measurement device firing photons on the electron, which is kinda lame because of course it isn't really the same experiment. Can we use a detector that doesn't influence the electrons? For example measure the change in a electromagnetic field by an electron to determine which slit it went through.
6 answers · 10 hours ago
• ### What is the term when you both have the same nuclear power?

6 answers · 1 day ago
• ### Can someone please give an example of an energy transformation in which kinetic energy is converted to work?

Best answer: A sailboat. The rapidly moving air ( containing kinetic energy) has its direction AND its speed altered by the boat. This gives a force and a distance to the boat causing it to move against the friction. The fluid clutch in an automatic transmission. One impeller pushes the fluid which gains speed and kinetic... show more
Best answer: A sailboat. The rapidly moving air ( containing kinetic energy) has its direction AND its speed altered by the boat.
This gives a force and a distance to the boat causing it to move against the friction.

The fluid clutch in an automatic transmission.
One impeller pushes the fluid which gains speed and kinetic energy.
This fluid ( containing kinetic energy) is then directed at a second impeller. This is pushed by the fluid causing the car to move forwards against friction.

In any turbine a fluid ( gas or liquid) passes blades or a propellor. The fluid changes direction and loses speed.
This causes the turbine to move against a load. ie it does work.

When I have a short but steep hill to surmount with my pushbike, I accelerate as I approach the bottom.
Giving my bike kinetic energy.
As the bike climbs the hill it slows down returning its energy in the form of work.
This adds to the work I am doing on the pedals so it increases the work available with which to climb the hill.

But WAIT, there's more.

I approach traffic lights in my car. I am going too fast. The kinetic energy of the car is turned into work at the brake pads. ( work = force * distance ) that work is converted to heat.
So in effect I was burning fuel a little while earlier for the purpose of overheating my brakes and wearing them out.
5 answers · 21 hours ago
• ### I'm not prone to beg. But I am begging for help for this physics question. I'm struggling with this one.?

Average voltage is equal to 2 * Peak Voltage / pi

2 * 2400 Volts / pi =>
(4800 / pi) Volts

V = I * R
2400 = 2 * R
1200 = R

(4800/pi) = 1200 * I
4/pi = I

Average voltage is equal to 2 * Peak Voltage / pi

2 * 2400 Volts / pi =>
(4800 / pi) Volts

V = I * R
2400 = 2 * R
1200 = R

(4800/pi) = 1200 * I
4/pi = I
5 answers · 21 hours ago
• ### If a spacecraft could use a limitless energy (i.e. fusion) to power it s engines, could it achieve light speed in space?

Best answer: no, for two reasons: 1. limitless energy does not give you reaction mass. To gain velocity, you have to throw away mass, taking advantage of conservation of momentum. More energy means you can toss the reaction mass away at high speed, but it's still not enough to get you very close to c. 2. No, light speed... show more
Best answer: no, for two reasons:

1. limitless energy does not give you reaction mass. To gain velocity, you have to throw away mass, taking advantage of conservation of momentum. More energy means you can toss the reaction mass away at high speed, but it's still not enough to get you very close to c.

2. No, light speed cannot be achieved, as it takes an infinite amount of energy to do that, even neglecting the reaction mass problem above.
9 answers · 3 days ago
• ### Is methane the chemical/gas that we should be most concerned with when it comes to global warming and climate change?

8 answers · 3 days ago
• ### Who has better physics? MIT or Harvard?

4 answers · 2 hours ago
• ### PHYSICS HELP!!!! EASY 10 POINTS?

A satellite in a circular orbit experiences a centripetal acceleration of 8.62m/s^2. The tangential speed of the satellite is 7.65 * 10^3 m/s. What is the altitude of the satellite? (r=6.38*10^6m)
A satellite in a circular orbit experiences a centripetal acceleration of 8.62m/s^2. The tangential speed of the satellite is 7.65 * 10^3 m/s. What is the altitude of the satellite? (r=6.38*10^6m)
4 answers · 3 hours ago
• ### Why does time exist? I love Albert Einstein’s comment that “the only reason for time is so that everything doesn’t happen at once.”?

Best answer: Entropy and the laws or thermodynamics is why. Entropy goes in only one direction. Entropy is increasing. the universe is becoming more unorganized and chaotic . Time goes in only ONE direction FORWARD.. if the Universe was static. it would not evolve. Whether YOU or ... show more
Best answer: Entropy and the laws or thermodynamics is why.

Entropy goes in only one direction. Entropy is increasing. the universe is becoming more unorganized and chaotic . Time goes in only ONE direction FORWARD.. if the Universe was static. it would not evolve. Whether YOU or Humans beings exist or NOT does NOT matter to the Universe. God DOES play dice with the Universe at subatomic and quark scales of size.. YOU would not exist without time time because the chemical reactions of metabolism and the electrical signals in your nervous system require TIME.. Time is an integral component of the universe. You CANNOT separate the temporal dimension from the spatial dimensions.

Time is an integral component of the Universe. it is N OT a concept invented by human beings HOW WE MEASURE time was invented by human, human beings DID NOT INVENT or create time.
10 answers · 7 days ago
• ### What is kinetic energy?

4 answers · 13 hours ago
• ### Hey if i drop my phone in the bath while it is on , is there a possibility that i could be electrocuted and die? thanks -dc?

17 answers · 6 days ago
• ### PHYSICS PROBLEM HELP?

Suppose NASA discovers a planet just like Earth and it is 35 light-years away from our Solar System. NASA quickly plans to send astronauts to this planet, but with the condition that the astronauts would not age more than 25 years during this journey. a) At what speed must the spaceship travel, in Earth's... show more
Suppose NASA discovers a planet just like Earth and it is 35 light-years away from our Solar System. NASA quickly plans to send astronauts to this planet, but with the condition that the astronauts would not age more than 25 years during this journey. a) At what speed must the spaceship travel, in Earth's reference frame, so that the astronauts age 25 years during this journey? b.) According to the astronauts, what will be the distance of their trip?
4 answers · 1 day ago
• ### If the external force acting on a system is zero, the momentum of the system is zero as well. True or False?

4 answers · 1 day ago
• ### What laws of physics prevent time travel to the past?

Best answer: One of the most interesting conclusions from special relativity can be best explained by an Einstein quote “the distinction between past, present, and future is a stubbornly persistent illusion”. That seems to drip with the possibility of time travel, but while fascinating, we are prevented from exploiting it by... show more
Best answer: One of the most interesting conclusions from special relativity can be best explained by an Einstein quote “the distinction between past, present, and future is a stubbornly persistent illusion”. That seems to drip with the possibility of time travel, but while fascinating, we are prevented from exploiting it by perhaps the most sacred law in physics - causality cannot be violated.

Einstein’s quote comes from the relativity of simultaneity between different inertial frames in special relativity. Two causally connected events in spacetime happen at different times in different reference frames. If the events are simultaneous in one reference frame, they are not simultaneous in another reference frame. If the events are simultaneous in the ‘present’ of one reference frame, they are not simultaneous in the present of other reference frames. One of the events will occur in the past or future of another reference frame depending on whether it is moving toward or away from the other frame. This negates the idea that there is any notion of absolute past or absolute future, e.g. things are done for everybody and haven’t happened for everybody. We cannot exploit this in relativity because we cannot MOVE FAST enough to violate the causal sequence of the two spacetime events. Special relativity prevents that.

General relativity is a different story. There can be extreme changes in the the geometry of spacetime due to extreme densities and distributions of matter and energy. There are solutions of general relativity, closed time curves and wormholes, that need to be discussed in the context of time travel.

Closed time curves are a similar idea to a closed loop in space, but the closed loop is time not space. These pop up in some solutions of General Relativity such as the Godel metric, which is a contrived metric for a rotating universe, with a contrived distribution of matter and energy. One of the issues with general relativity is that it is ignorant about certain other laws of physics. For instance, general relativity is time symmetric, it does not know about entropy, quantum mechanics, and it has issues with energy conservation. So, while closed time curves are allowed, they are likely non-physical solutions prevented by other laws of physics such as entropy and energy conservation.

Wormholes are always a fun, controversial subject. They are also allowed solutions to general relativity and I’m not going to go into details since I haven’t seen anybody on YA that understands wormhole metrics so it would be a waste of time to go into any detail. Suffice to say that solutions of General Relativity can be found that include wormholes, but the wormholes connect two separate ‘flat’ spacetime regions. General Relativity cannot tell us whether those flat regions are two separate regions of our universe or regions of two separate universes. So, in order to preserve causality, IF somehow a traversable wormhole could be constructed, the requirement for preservation of causality would mean that the two regions are in separate universes and no time travel could actually occur, and hence no causality violations.
13 answers · 1 week ago